Ceramic and cement-bodied tiles are the hardest and most durable members of the tile family.
The term ceramic refers to any hard-bodied material made chiefly from clay and hardened by firing at high temperatures. Most modern ceramic tiles contain a mixture of refined clay, ground shale or gypsum, and other ingredients that reduce the shrinkage of the tile as it's fired.
Once mixed with water, the clay body of the tile (or its bisque) gets its shape by being squeezed into a mold, pressed into a die, or cut like cookies from sheets. From there, temperatures from 900 degrees F to 2,500 degrees F harden the bisque. Most ceramic tiles are fired at about 2,000 degrees F. In general, higher temperatures produce a denser tile. Most unglazed tiles are fired only once, but some are fired twice. Those with decorative glazes are fired up to five times. The more firings, the higher the cost.
In addition to high-fired clay products, you'll find a host of other hard-bodied tiles. Some, such as brick veneer, originate from clay mixtures fired at lower temperatures than ceramic tiles. Others, such as saltillo tiles, are handmade from unrefined clay and bonding agents and don't get fired at all -- they are sun-dried or allowed to dry in low-temperature kilns. Cement-bodied tiles are made from a mortar-and-sand mix that cures in a chemical reaction.
Some of these non-ceramic varieties have specific uses and a few restrictions. For example, most imitation brick veneer is too soft for floors but is a great choice for walls. Handmade tiles, such as saltillo, have a rough texture. Their natural imperfections can add rustic charm, but they also absorb water readily. That relegates them to indoor use, and they still require sealing. Cement-bodied tiles are a less expensive, long-lasting look-alike for ceramics that work well in many kinds of applications.
Quarry tile, extruded and fired at high temperatures, is semivitreous or vitreous. Made in 1/2 to 3/4 inch thicknesses, it is fired unglazed with bisques in many colors, sizes, and shapes, such as 4- to 12-inch squares and hexagons, and 3x6-inch or 4x8-inch rectangles.
Porcelain tile, made of highly refined clay and fired at extremely high temperatures, absorbs virtually no moisture. Porcelain tiles may be glazed or unglazed. Sizes range from 1x1-inch mosaics to large 24x24-inch pieces, some with stone-look patterns.
Terra-cotta tile, though technically not a ceramic because it is fired at low temperatures, is a low-density, nonvitreous tile suitable for dry areas. Its surface defects add to its charm. Available sealed or unsealed, it comes in squares from 3 to 12 inches and in other geometric shapes.
Cement-bodied tile, a cured sand-and-mortar mix, is a nonvitreous tile with excellent durability. Some tiles look rough-hewn, others sport smooth finishes. Available in squares or rectangles from about 6 to 9 inches and in mesh-backed paver sheets (up to 36 inches) that mimic cleft stone.
Saltillo tile is not a true ceramic tile because it is dried not fired. Nevertheless it is treated as a ceramic tile and enjoys wide use in rustic and Southwestern designs. Available in squares, rectangles, octagons, and hexagons, from 4 to 12 inches, it is a low-density, nonvitreous product.
Tile varies in its ability to absorb water, and its vitreosity should be a factor in choosing tile for different locations.
Nonvitreous tile can absorb more than 7 percent of its weight in water and is not suitable for areas that will get wet.
Semivitreous tile has an absorption rate of 3 to 7 percent -- good for family rooms but not desirable for outdoor use.
Vitreous tile is dense; it absorbs only 0.5 to 3 percent of its weight in water. You can install it in almost any location.
Impervious tile is almost completely water-resistant. It is more commonly found in hospitals, restaurants, and other commercial installations rather than residential settings.
Glazes made of lead silicates and pigments brushed or sprayed onto the surface of the tile add both color and protection. Some glazes are applied to the bisque before it's fired. Others go on after the first firing and are fired again. Single-fired tiles exhibit greater strength and durability. Additives introduced to the glaze will provide texture to the surface of the tile.
Glazed tiles are water-resistant, but the grout joints between them are not. Even when grouting tiles with a latex- or polymer-modified grout, you should seal the joints.
Unglazed tiles soak up water and always need sealing to prevent damaging the adhesive or surface below.
As you make decisions about tile purchases, you may encounter the following terms associated with tile manufacturing:
-- Bisque: The clay body of the tile. Bisque that is "green" has not yet been fired.
-- Cured: Describes bisque dried naturally or in low-temperature kilns.
-- Extruded: A process in which wet clay is squeezed under pressure into a mold.
-- Fired: Bisque hardened in high temperatures.
-- Glaze: A hard, thin layer of pigment applied to the tile to give it color and protection.
-- Vitreosity: The resistance of a tile to water absorption, ranging from nonvitreous (very absorbent) to impervious (almost completely water-resistant).